Apparatus for directional control of a drilling tool

ABSTRACT

A directional-control apparatus for a drilling tool, in which the direction of the drilling tool during the drilling of a borehole is controlled by means of at least one steering body which is moved radially against the wall of the borehole, the movement of the at least one steering body relative to the centre axis of the directional-control apparatus being adjustable in order to steer the drilling tool in a desired direction and at a desired deflection, and at least one electrically operated actuator being connected via at least one set of transmission elements to the at least one steering body and arranged to move the at least one steering body into a position relative to the centre axis of the directional-control apparatus, the relative position having the effect that the drilling tool is steered in the desired direction and at the desired deflection.

This application is a Continuation of U.S. Ser. No. 13/665,132, which isa National Stage Application of PCT/NO2008/000224, filed 18 Jun. 2008,which claims benefit of Ser. No. 20073136, filed 20 Jun. 2007 in Norwayand which applications are incorporated herein by reference. To theextent appropriate, a claim of priority is made to each of the abovedisclosed applications.

This invention relates to a directional-control apparatus for a drillingtool. More particularly, it relates to a directional-control apparatusfor a drilling tool in which the direction of the drilling tool duringthe drilling of a borehole is controlled by means of at least onesteering body which is moved radially against the wall of the borehole.The movement of the at least one steering body relative to the centreaxis of the directional-control apparatus is adjustable with respect tosteering the drilling tool in a desired direction and at a desireddeflection. At least one electric actuator is connected via at least oneset of transmission elements to the at least one steering body and isarranged to move the at least one steering body into a position relativeto the centre axis of the directional-control apparatus, the relativeposition of the at least one steering body causing the drilling tool tobe steered in the desired direction and at the desired deflection.

During drilling in the ground as it is known from the recovery ofpetroleum among other things, it is often necessary to be able to steerthe drilling tool in a desired direction. For example, so-calleddeviation wells are drilled with considerable deviation from thevertical direction.

During drilling in the ground it is common to use a drill bit which isconnected to a pipe string, the pipe string and drill bit being rotatedabout their longitudinal axes by a drilling device at the surface.

According to the prior art, the directional control of the drilling toolmay be exerted by applying to the drill bit a radial force which isarranged to make the drill bit drill at some deflection in a desireddirection relative to its centre axis. Instrumentation at the drill bitin the form of at least a gyroscope, an accelerometer, or amagnetometer, enables feedback on the position of the drill bit in theground.

US patent application 2006/0090935 discloses a number of bodies whichare arranged in an intermediate piece between the drill bit and the pipestring, the bodies being manoeuvred by means of hydraulic pistons.Transducers measure the positions of the respective pistons, hydraulicvalves being used to control the pressure on the bodies, whereby theradial force from the bodies against the borehole wall has the effect ofsteering the drill bit in the desired direction. Thus, the deviceaccording to US 2006/0090935 is relatively complicated with relativelymany valves which will be sensitive and which are supplied with drillingfluid under pressure as the operating means.

The invention has for its object to remedy or to reduce at least one ofthe drawbacks of the prior art.

The object is achieved through features which are specified in thedescription below and in the claims that follow.

A directional-control apparatus in accordance with the invention for thedirectional control of a drilling tool, in which the direction of thedrilling tool during drilling is controlled by means of at least onesteering body which is moved radially against the borehole wall, and inwhich the movement of the at least one steering body relative to thecentre axis of the directional-control apparatus is adjustable withrespect to steering the drilling tool in a desired direction and at adesired deflection. The directional-control apparatus according to theinvention is characterized by at least one electric actuator beingconnected via at least one set of transmission elements to the at leastone steering body and being arranged to move the at least one steeringbody into a position relative to the centre axis of thedirectional-control apparatus, the relative position having the effectthat the drilling tool is moved in the desired direction and at thedesired deflection.

The at least one electric actuator is typically supplied with energy viaa wire connection to the surface, but it may also be supplied withenergy from a local accumulator or a drilling-fluid-operated generator,for example. The actuator may communicate with the surface via knowncommunication methods.

With advantage, the first electric actuator is connected to the at leastone steering body via a first set of transmission elements and arrangedto move the at least one steering body into a position relative to thecentre axis of the directional-control apparatus, the relative positionhaving the effect that the drilling tool is steered at the desireddeflection, and a second electric actuator being connected via a secondset of transmission elements to the at least one steering body andarranged to move the at least one steering body into a position relativeto the centre axis of the directional-control apparatus, the relativeposition having the effect that the drilling tool is steered in thedesired direction.

The directional-control apparatus, including, in a manner known per se,an intermediate housing, is positioned between the drill bit and pipestring of the drilling tool immediately behind the drill bit.

With advantage, the intermediate housing is rotating freely in relationto the pipe string and is thereby not co-rotating with the pipe stringduring drilling. A mandrel, which is connected to the pipe string and tothe drill bit, extends centrically through the intermediate housing,transferring torque and drilling fluid, among other things.

In a preferred embodiment the directional-control apparatus includes anumber of steering bodies which are spaced around the intermediatehousing, and which are movable in a radial direction relative to thecentre axis of the directional-control apparatus and, thereby, that ofthe drilling tool. An inner eccentric sleeve is rotatably supportedaround the mandrel and is surrounded by an outer eccentric sleeve. Theouter eccentric sleeve and the inner eccentric sleeve have equaldifferences between their respective largest and smallest externalradii. The external cylinder surface of the outer eccentric sleeve isthereby concentric with the centre axis of the directional-controlapparatus when the largest radius of the eccentric sleeve is at 180degrees relative to the largest radius of the internal eccentric sleeve.

When the steering bodies are to be moved in a particular direction inorder to change the direction of drilling of the drill bit, the outereccentric sleeve is rotated by means of the first actuator until thesteering bodies have been given a desired displacement. The internaleccentric sleeve is rotated together with the outer eccentric sleeveuntil the largest diameter of the outer eccentric sleeve is in thedesired direction relative to the centre axis of the apparatus. Thisdirection is normally diametrically opposite the direction in which thedrill bit is to be steered.

The electric actuators may, with advantage, be constituted by electricmotors. The actuators may be provided with positioners of a design knownper se.

Electrical control and actuation of the at least one steering body ofthe directional-control apparatus lead to the directional-controlapparatus being independent of hydraulic fluid, whether in the form ofdrilling fluid, which may exhibit relatively great pressure variations,or from a local fluid reservoir with the necessary pump equipment. Thus,the invention provides a substantial simplification in relation to theprior art devices for the directional control of a drilling tool.

In what follows, is described an example of a preferred embodiment whichis visualized in the accompanying drawings, in is which:

FIG. 1 shows a drilling tool including a pipe string and a drill bit andalso a directional-control apparatus in accordance with the invention;

FIG. 2 shows, on a larger scale, a longitudinal section of thedirectional-control apparatus according to FIG. 1;

FIG. 3 shows, on a somewhat further enlarged scale, a section IIa-IIa ofFIG. 2, in which the directional-control apparatus steers the drillingtool in a direction A;

FIG. 4 shows a section IIb-IIb of FIG. 2 under the same conditions asthose of FIG. 3;

FIG. 5 shows the section IIa-IIa of FIG. 2, but after thedirectional-control apparatus has been adjusted into a neutral position;

FIG. 6 shows the section IIb-IIb of FIG. 2 under the same conditions asthose of FIG. 5; and

FIG. 7 shows the section IIa-IIa of FIG. 2 after the directional-controlapparatus has been adjusted to steer the drilling tool in a direction B.

In the drawings the reference numeral 1 denotes a drilling tool whichincludes a drill string 2 and also a drill bit 4, and in which there isinstalled between the pipe string 2 and the drill bit 4 adirectional-control apparatus 6 by means of an adapter sleeve 8.

The directional-control apparatus 6 includes an intermediate housing 10with a centre axis 12 and a concentric through mandrel 14. The mandrel14 is sealingly connected, at its one end portion, to the drill bit 4and sealingly connected, at its opposite end portion, to the pipe string2 by means of the adapter sleeve 8. A nut 16 holds the mandrel 14 inposition in the adapter sleeve 8.

The mandrel 14 is provided with a centric bore 18 extending through itfor drilling fluid to flow through from the pipe string 2 to the drillbit 4. The intermediate housing 10 is connected to the mandrel 14 viabearings 20 and rotates freely about the mandrel 14.

A first steering body 22′, a second steering body 22″ and a thirdsteering body 22″′, see FIG. 3, are spaced, radially movable, atpreferably equal divisions around the intermediate housing 10. Thesteering bodies 22′, 22″, 22′″ are cylinder-shaped, fittingcomplementarily into their respective bores 24 in the intermediatehousing 10.

At their end portions facing the centre axis 12, the steering bodies22′, 22″, 22″′ bear on an outer eccentric sleeve 26, the outer eccentricsleeve 26 being rotatably supported around an inner eccentric sleeve 28.The outer eccentric sleeve 26 and the inner eccentric sleeve 28 haveequal differences between their respective largest and smallest externalradii.

A hook 30 in each of the steering bodies 22′, 22″, 22″′ projects axiallyrelative to the centre axis 12 into a groove 32 surrounding the outereccentric sleeve 26. Thereby, the steering bodies 22′, 22″, 22′″ areprevented from being moved inadvertently out of the intermediate housing10.

In its end portion facing away from the drill bit 4, the outer eccentricsleeve 26 is provided with an internal gear rim 34 which is concentricwith the inner jacket surface 36 of the outer eccentric sleeve 26.

The inner eccentric sleeve 28 supportedly and rotatably surrounds themandrel 14, an extension sleeve 38, connected to the inner eccentricsleeve 28, projecting axially from the end portion of the innereccentric sleeve 28 facing away from the drill bit 4.

A gear 40 supportingly surrounding the extension sleeve 38complementarily matches the gear rim 34 and is connected to a firstelectric motor forming a first electrically operated actuator 42. Thefirst actuator 42 is attached to the extension sleeve 38, co-rotatingtherewith. The first actuator 42 is arranged to rotate the outereccentric sleeve 26 around the inner eccentric sleeve 28.

The engagement of the gear 40 with the gear rim 34 remains satisfactoryeven if the centre of the gear rim 34 is moved about the centre axis 12when the inner eccentric sleeve 28 is rotated, as the centre of the gearrim 34 coincides with the centre of the external jacket 44 of the innereccentric sleeve 28.

The extension sleeve 38 is connected to a second electric motor forminga second electrically operated actuator 46. The second actuator 46 isattached to the intermediate housing 10. Thereby, the second, actuator46 is arranged to rotate the extension sleeve 38 with the innereccentric sleeve 28 relative to the intermediate housing 10.

The actuators 42, 46 are supplied with energy and control signals via awire connection 48 extending to the surface.

The outer eccentric sleeve 26 and the gear 40 form a first set oftransmission elements 50, whereas the inner eccentric sleeve 28 with theextension sleeve 38 forms a second set of transmission elements 52.

By rotating the outer eccentric sleeve 26 about the inner eccentricsleeve 28 by means of the first actuator 42, the outer eccentricity ofthe outer eccentric sleeve 26 relative to the centre axis 12 may beadjusted between zero and full deflection. In FIGS. 3 and 4 the outereccentric sleeve 26 is approximately at full deflection, whereas inFIGS. 5 and 6 it is shown in a concentric position relative to thecentre axis 12. Thus, the first actuator 42 is used to control thedisplacement or admission of the steering bodies 22′, 22″, 22′″.

The second actuator 46 rotates the inner eccentric sleeve 28 and theouter eccentric sleeve 26 and the first actuator 42 around the centreaxis 12 relative to the intermediate housing 10. In principle, theintermediate housing 10, which is freely supported, does not rotate,even if the pipe string 2, adapter sleeve 8, mandrel 14 and drill bit ,4are rotating. Thus, the second actuator is used to set the direction inwhich the steering bodies 22′, 22″, 22″′ are to direct the drill bit,see FIG. 3, in which the drill bit 4 is directed in a direction A, andFIG. 7, in which the drill bit 4 is directed in a direction B.

However, in practice, because of frictional forces and vibrations, theintermediate housing 10 will be dragged along somewhat in the rotationduring drilling. The second actuator 46 compensates for this by rotatingthe eccentric sleeves 26, 28 correspondingly in the opposite direction.

1. A directional-control apparatus for a drilling tool, thedirectional-control apparatus comprising: a centre axis; an intermediatehousing, wherein at least one steering body fits into a respective borein the intermediate housing being adjustable in a radial directionrelative to the intermediate housing and against a wall of a borehole,the at least one steering body, at an end portion facing the centreaxis, being supported on an outer eccentric sleeve which is rotatablysupported on an inner eccentric sleeve which is rotatably supported on amandrel; a first electrically operated actuator for rotation of theouter eccentric sleeve; and a second electrically operated actuator forrotation of the inner eccentric sleeve and the outer eccentric sleeve,wherein the drilling tool is steered in a desired direction and at adesired deflection.
 2. The directional-control apparatus according toclaim 1, wherein the at least one steering body is provided with a hookwhich projects axially relative to the centre axis and into a groove inthe outer eccentric sleeve.
 3. The directional-control apparatusaccording to claim 1, wherein the first electrically operated actuatorand the second electrically operated actuator are connected to a wireconnection to receive control signals and a supply of energy, whereinthe wire connection extends to a surface.
 4. The directional-controlapparatus for a drilling tool, the directional-control apparatuscomprising: a centre axis and an intermediate housing, wherein at leastone steering body fits into a bore in the intermediate housing beingadjustable in a radial direction relative to the intermediate housing ofthe directional-control apparatus and against a wall of a borehole, theat least one steering body, at an end portion facing the centre axis,being supported on an outer eccentric sleeve which is rotatablysupported on an inner eccentric sleeve which is rotatably supported on amandrel.
 5. The directional-control apparatus according to claim 4,wherein the directional-control apparatus further comprises a firstelectrically operated actuator for rotation of the outer eccentricsleeve and a second electrically operated actuator for rotation of theinner eccentric sleeve and the outer eccentric sleeve.
 6. Thedirectional-control apparatus according to claim 4, wherein the at leastone steering body is provided with a hook which projects axiallyrelative to the centre axis and into a groove in the outer eccentricsleeve.
 7. The directional-control apparatus according to claim 4,wherein the first electrically operated actuator and the secondelectrically operated actuator are connected to a wire connection toreceive control signals and a supply of energy, wherein the wireconnection extending to the surface.
 8. The directional-controlapparatus according to claim 1, wherein the first electrically operatedactuator and the second electrically operated actuator are connected toa wire connection to receive control signals and a supply of energy,wherein the energy is supplied from a local accumulator or drillingfluid-operated generator, wherein the first or second electricallyoperated actuator communicates with a surface system.